Democritus (460 - 370 BC) was a Greek philosopher, who developed the atomic theory of the universe, which had been originated by his mentor, the philosopher Leucippus. Democritus was born in Abdera, Thrace. He wrote extensively, but only fragments of his works remain. According to his exposition of the atomic theory of matter, all things are composed of minute, invisible, indestructible particles of pure matter (atoma, "indivisibles"), which move about eternally in infinite empty space (kenon, "the void")